dge. Terrestrial
analysis had failed to furnish favorable evidence; and, turning to the
chemistry of the stars, the spectra of the white, which were
presumably the hottest stars, furnished no direct evidence that a
decomposition of any terrestrial atom had taken place; indeed, we
learned that the hydrogen atom, as we know it here, can endure
unscathed the inconceivably fierce temperature of stars presumably
many times more fervent than our sun, as Sirius and Vega. It was
therefore no matter for surprise if the earth-bound chemist should for
the present continue to regard the elements as the unalterable
foundation stones upon which his science is based.

ATOMIC MOTION.

Passing to the consideration of atoms in motion, while Dalton and
Graham indicated that they were in a continual state of motion, we
were indebted to Joule for the first accurate determination of the
rate of that motion. Clerk-Maxwell had calculated that a hydrogen
molecule, moving at the rate of seventy miles per minute, must, in one
second of time, knock against others no fewer than eighteen thousand
million times. This led to the reflection that in nature there is no
such thing as great or small, and that the structure of the smallest
particle, invisible even to our most searching vision, may be as
complicated as that of any one of the heavenly bodies which circle
round our sun. How did this wonderful atomic motion affect their
chemistry?

ATOMIC COMBINATION.

Lavoisier left unexplained the dynamics of combustion; but in 1843,
before the chemical section of the association meeting at Cork, Dr.
Joule announced the discovery which was to revolutionize modern
science, namely, the determination of the mechanical equivalent of
heat. Every change in the arrangement of the particles he found was
accompanied by a definite evolution or an absorption of heat. Heat was
evolved by the clashing of the atoms, and this amount was fixed and
definite. Thus to Joule we owe the foundation of chemical dynamics and
the basis of thermal chemistry. It was upon a knowledge of the mode of
arrangement of atoms, and on a recognition of their distinctive
properties, that the superstructure of modern organic chemistry
rested. We now assumed on good grounds that the atom of each element
possessed distinct capabilities of combination. The knowledge of the
mode in which the atoms in the molecule are arranged had given to
organic chemistry an impetus which had overcome many